A week after his razor-thin victory in Iowa, Republican presidential hopeful Mitt Romney is leading in New Hampshire but the gap is shrinking.

The candidates faced a double-header debate over the weekend, with the frontrunner accused of "pious baloney" and ridiculed for claiming he is not a career politician.

Mr Romney's rivals hammered him, knowing a win in New Hampshire will increase the perception he is the inevitable candidate.

He remains the frontrunner although the latest tracking poll shows his support slipping four points to 35 per cent as he faces attacks from rivals painting him as a timid moderate.

In a shot at Newt Gingrich and former senator Rick Santorum, a devout Christian conservative, Mr Romney said "someone who isn't a lifelong politician" would have a better shot at beating Barack Obama and underlined "we've got to nominate a leader".

"This for me, politics, is not a career. For me, my career was being in business and starting a business and making it successful. My life's passion has been my family, my faith and my country," he said.

That sparked a tetchy exchange with Mr Gingrich, the former House speaker.

"Can we drop a little bit of the pious baloney. You've been running consistently for years and years and years," he said.

"So this idea that suddenly citizenship showed up in your mind, just level with the American people. You've been running at least since the 1990s."

Mr Santorum pointed to Mr Romney's decision not to run for re-election as governor in the face of poor poll numbers and thundered: "We want someone, when the time gets tough - and it will in this election - we want someone who's going to stand up and fight for the conservative principles, not bail out and not run."

Can we drop a little bit of the pious baloney. You've been running consistently for years and years and years.

Newt Gingrich to rival Republican presidential hopeful Mitt Romney

The former senator, who is hoping to build on his success in Iowa, also came down hard on Ron Paul, questioning how little he had been able to change on Capitol Hill.

"One of the reasons people like congressman Paul is his economic plan. He has never been able to accomplish any of that," he said.

"He has no track record of being able to work together. He has been out there on the margins and has really been unsuccessful in working together with anybody."

The Texas congressman is coming in second in the latest polls on 20 per cent.

Lead narrows

While the attacks amounted to a sharp escalation in tone against Mr Romney, he gave as good as he got and committed no major errors, making it unlikely the assault would derail his better-funded, better-organised campaign.

His vast campaign war chest and high-profile endorsements have fed his image as the candidate to beat, but he faces stubborn doubts about his conservative credentials and has never been able to push his support from Republicans nationwide above 30 per cent.

Former US envoy to China Jon Huntsman scored one of the biggest applause-getting lines of the debate when he rebuked Mr Romney for attacking his service as Mr Obama's first ambassador to China.

"Yes, [I served] under a Democrat like my two sons are doing in the United States Navy," he said.

"They are not asking who, what political affiliation the president is. I want to be very clear with the people here in New Hampshire in this country - I will always put my country first and I think that's important to them."

Mr Romney retaliated, saying "the person who should represent our party running against president Obama is not someone who called him a remarkable leader and went to be his ambassador in China".

But Mr Huntsman won more applause when he shot back to NBC moderator David Gregory: "This nation is divided, David, because of attitudes like that. The American people are tired of the partisan division. They have had enough."

The primary will be the first time he faces voters, after the former Utah governor did not compete in Iowa, concentrating his efforts on the more moderate state of New Hampshire.

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